1. Field of the Invention
The present invention relates to a magnetoresistive head for reproducing information magnetically stored, a method for manufacturing the magnetoresistive head, and a magnetic recording device having the magnetoresistive head, and more particularly to a magnetoresistive head having a high reproduction output and a magnetic recording device having the magnetoresistive head having the high reproduction output.
2. Description of the Related Art
A recording density of a magnetic recording device has been remarkably increased. It has been requested that a magnetoresistive head provided in the magnetic recording device have a smaller track width and have a high recording property and a high reproducing property. For the high reproducing property, a magnetoresistive head using a magnetoresistive effect has been developed to increase sensitivity of the head. When a recording density is low and approximately several gigabytes per square inch, anisotropic magnetoresistive effect (AMR) has been used to convert a magnetic signal on a recording medium into an electrical signal. When the recording density is higher than the aforementioned value, a giant magnetoresistive effect (GMR) with higher sensitivity is used.
For the request to increase the recording density, a current perpendicular to plan scheme has been researched and developed since a distance (reproduction gap length) between an upper magnetic shield layer and a lower magnetic shield layer has tended to be reduced. The current perpendicular to plan (CPP) scheme has an advantage to increase the sensitivity. In the current perpendicular to plan scheme, a detection current flows in a direction substantially perpendicular to the surface of a film. A magnetic reproduction head using a CPP GMR and a magnetic reproduction head using a tunneling magnetoresistive effect have been reported.
The basic structure of a CPP magnetic reproduction head is described below with reference to FIGS. 1 and 2. FIG. 1 is an outline cross sectional view of the CPP magnetic reproduction head, taken along a direction parallel to a surface of the CPP magnetic reproduction head (or taken along a direction perpendicular to the direction of the height of an element). The surface of the CPP magnetic reproduction head faces a surface of a recording medium and is hereinafter referred to as a medium facing surface. An X axis shown in FIG. 1 is parallel to the direction of a track width of the CPP magnetic reproduction head. A Y axis shown in FIG. 1 is parallel to the direction of the height of the element. A Z axis shown in FIG. 1 is parallel to the direction of the thickness of a magnetoresistive effect film 3. In each of the accompanying drawings following FIG. 1, X, Y and Z indicate the same directions as those of the X, Y and Z axes shown in FIG. 1, respectively. The track width is denoted by an arrow T. A track width direction refill film 1 is in contact with a side wall surface in the direction of the track width of the magnetoresistive effect film 3 as shown in FIG. 1. The magnetoresistive effect film 3 is composed of a fixed layer 31, an insulating barrier layer 32 and a free layer 33. The insulating barrier layer 32 is located between the fixed layer 31 and the free layer 33. A vertical bias application or a side shield layer 5 is not necessarily required. In FIG. 1, reference numeral 2 denotes an upper magnetic shield layer, and reference numeral 4 denotes a lower magnetic shield layer. FIG. 2 is a cross sectional view of the CPP magnetic reproduction head in the direction of the height of the element, taken along line a-a′ of FIG. 1. The right side of FIG. 2 indicates the medium facing surface of the magnetic reproduction head. The medium facing surface of the magnetic reproduction head is denoted by reference numeral 112. An element height direction refill film 6 is in contact with a wall surface of the magnetoresistive effect film 3. Alumina, which is an insulating film, is mainly used as a material of the track width direction refill film 1 and a material of the element height direction refill film 6.
The CPP magnetic reproduction head is typically formed to ensure that the magnetoresistive effect film 3 is in electrical contact with the upper magnetic shield layer 2 and the lower magnetic shield layer 4 in order to reduce the reproduction gap length as much as possible. The upper magnetic shield layer 2 and the lower magnetic shield layer 4 serve as electrodes adapted to cause a current to flow in the magnetoresistive effect film 3. When a circuit exists to electrically short the upper and lower magnetic shield layers 2 and 4 except for the magnetoresistive effect film 3, the circuit may serve as a path for leaking a detection current. This may reduce output of the magnetic reproduction head.
The short circuit may be formed at the side wall surface of the magnetoresistive effect film 3. This is relevant with a method for forming the magnetic reproduction head. FIGS. 3A and 3B are flowcharts showing two types of processes for manufacturing the magnetic reproduction head. Each of the processes for manufacturing the magnetic reproduction head has a step for forming the lower magnetic shield layer, a step for forming the magnetoresistive effect film, a step for adjusting the magnetoresistive effect film, and a step for forming the upper magnetic shield layer. A difference between the process shown in FIG. 3A and the process shown in FIG. 3B is the order of the step for adjusting the magnetoresistive effect film in the direction of the height of the element and the step for adjusting the magnetoresistive effect film in the direction of the track width. This order varies depending on the situation. The step for adjusting the magnetoresistive effect film in the direction of the height of the element may be performed before the step for adjusting the magnetoresistive effect film in the direction of the track width. The step for adjusting the magnetoresistive effect film in the direction of the track width may be performed before the step for adjusting the magnetoresistive effect film in the direction of the height of the element.
In the step for adjusting the magnetoresistive effect film in the direction of the height of the element and the step for adjusting the magnetoresistive effect film in the direction of the track width after the step for forming the magnetoresistive effect film, the magnetoresistive effect film 3 is protected by a resist mask 101 having a predetermined size as shown in FIG. 4A. An unnecessary portion of the magnetoresistive effect film 3 is etched as shown in FIG. 4B. In this etching step, an ion beam etching method using an Ar ion, or a reactive ion etching (RIE) method using a chlorine-based gas or a CO-based gas is typically performed. After the etching, the element height direction refill film 6 or the track width direction refill film 1 is formed as shown in FIG. 4C. Then, the resist mask 101 and an unnecessary portion of the refill film(s) are removed by a lift-off method to adjust the magnetoresistive effect film 3 in the direction of the height of the element and in the direction of the track width as shown in FIG. 4D. In the step for adjusting the magnetoresistive effect film 3 in the direction of the track width, the side shield layer or the vertical bias application layer (not shown in FIGS. 4A to 4D) may be formed on the track width direction refill film 1.
During the etching shown in FIG. 4B, the etched portion may be reattached to the wall surface of the magnetoresistive effect film 3. This effect is called reattachment. The re-attached film forms a film made of a metal constituting a part of the magnetoresistive effect film 3 or a part of the lower magnetic shield layer 4, and has a conductive property. Therefore, the re-attached film may serve as a path for leaking the detection current.
JP-A-2003-86861 discloses a method for oxidizing a re-attached film after etching in the step for adjusting the magnetoresistive effect film 3 in the direction of the track width to prevent a detection current from leaking due to reattachment of the substance to the wall surface of the magnetoresistive effect film 3. This method is characterized in that the re-attached film functions as a part of the track width direction refill film due to the oxidization.
JP-A-2002-26423 discloses a method for removing a substance reattached to the wall surface of the magnetoresistive effect film 3. In this method, during the etching shown in FIG. 4B, a predetermined portion of the magnetoresistive effect film 3 formed on the lower magnetic shield layer 4 is masked by a resist mask used for adjustment of the magnetoresistive effect film 3 in the direction of the track width and by a resist mask used for adjustment of the magnetoresistive effect film 3 in the direction of the height of the element. An ion beam is incident on the magnetoresistive effect film 3 at a first incident angle θ1 with respect to a normal to the surface of the magnetoresistive effect film 3 to etch a portion of the magnetoresistive effect film 3. After the etching, an ion beam is incident on the magnetoresistive effect film 3 at a second incident angle θ2 (θ2>θ1) with respect to the normal to the surface of the magnetoresistive effect film 3 to remove the substance reattached to the wall surface of the magnetoresistive effect film 3. In this case, each of the incident angles is formed between the incident direction of the ion beam and a normal to the surface of a substrate.
JP-A-2006-24294 discloses an advanced method compared with the aforementioned method for the two-step etching technique. In the method disclosed in JP-A-2006-24294, a first refill film and a second refill film having lower hardness than that of the first refill film are used to ensure that there is not an area in which an ion beam for removal of a re-attached film is hardly incident on the magnetoresistive effect film 3.